The present invention is based on the discovery that certain oxadiazolone compounds, some of which are described in Tett. Lett. (44) pp. 3875-3878 (1974), can be employed as foaming agents in high temperature thermoplastic polymers such as polycarbonate, polysulfone and the like. Other blowing agents, such as 5-phenyltetrazol and benzamides (U.S. Pat. No. 3,781,233 and U.S. Pat. No. 3,779,954) and dioxazolones (U.S. Pat. No. 4,288,560) although effective foaming agents for polycarbonate, cause degradation of the resin during the foaming process. The principal technical advantage of the present oxadiazolone derivatives is, therefore, the fact that less degradation of the resin results during foaming.
The art is noted to include U.S. Pat. Nos. 4,097,425 and 4,163,037 which disclose dihydrooxadiazinones as chemical blowing agents, as well as U.S. Pat. No. 4,263,409 which discloses chemical containing decomposable groups such as azo, N-nitroso, carboxylate, carbonate, heterocyclic nitrogen containing and sulfonyl hydrazide groups, as suitable foaming agents.
The azole derivatives of the present invention are noted for their improved compatibility with the resin upon foaming as expressed in the virtual elimination of resin degradation.